#include <iostream>
#include <queue>
#include <vector>

using namespace std;

int main() {
    int n, m;
    cin >> n >> m;

    vector<vector<int>> graph(n);

    while (m--) {
        int a, b;
        cin >> a >> b;

        a--;
        b--;

        graph[a].push_back(b);
        graph[b].push_back(a);
    }

    queue<int> q;
    vector<int> d(n, -1);
    vector<bool> v(n);
    vector<int> p(n, -1);

    q.push(0);
    d[0] = 1;
    p[0] = 0;

    while (!q.empty()) {
        int a = q.front();
        q.pop();

        v[a] = true;

        for (int x : graph[a]) {
            if (!v[x]) {
                if (d[x] == -1) {
                    d[x] = d[a] + 1;
                }

                if (p[x] == -1) {
                    p[x] = a;
                }

                q.push(x);
            }
        }
    }

    if (d[n - 1] == -1) {
        cout << "IMPOSSIBLE" << endl;
    } else {
        cout << d[n - 1] << endl;

        vector<int> solution;

        int i = n - 1;
        while (i != p[i]) {
            solution.push_back(i + 1);
            i = p[i];
        }

        solution.push_back(i + 1);

        for (auto j = solution.end() - 1; j >= solution.begin(); j--) {
            cout << *j << " ";
        }

        cout << endl;
    }
}